A typical bedding mattress foundation or so called "box spring", or box spring assembly, comprises a rectangularly-shaped structure of substantially uniform thickness having an outer, upholstered cloth cover. The structure has sufficient resiliency to compress upon application of a force, such as the weight of a person sitting or reclining, yet it also has sufficient rigidity to return to an uncompressed state when the force is removed.
Within the cloth cover, a box spring usually has a rigid peripheral frame which is connected to a plurality of internal springs, which are typically made of wire. Together, the springs and the frame form an internal lattice for the box spring. This lattice provides sufficient rigidity and structural integrity for maintaining the rectangular shape, with the springs providing the necessary resiliency. Within this lattice, the springs must be connected to the members which comprise the peripheral frame, and the springs must be connected such that they remain connected over a long period of use.
Because of the need to connect the springs to these other members of the lattice, the construction of a box spring, and particularly the internal lattice of the box spring, is relatively time consuming and labor-intensive. This is particularly true if stapled connections must be made or if mechanical fasteners are necessary to connect the springs to the frame.
In some box spring structures, intermediary pieces are used to interconnect the springs to the lattice members at one or both ends of the springs. For instance, Mandusky et al. U.S. Pat. No. 3,888,474 discloses a retention clip for interconnecting one end of an internal spring to a metal frame rail of a box spring, wherein one side of the retention clip is readily mountable to and slidable along the frame rail, and the other side of the clip is adapted to hold one end of a wire spring. This slidable retention clip enables the use of any desired number of springs and eliminates the need to staple the clip and/or the spring to the frame rail, or the need to use additional fasteners to secure the retention clips and/or the springs to the frame rails.
The clip disclosed in this patent appears to solve some of the construction problems associated with forming a lattice for a box spring. However, the retention clip shown in FIG. 3 of this patent is secured to a rail edge at only one end of the retention clip. The other end of the clip simply rests on the opposite side of the rail. This free end of the clip appears susceptible to vertical movement as the spring attached thereto is vertically compressed and extended, as is common over a period of use. This could eventually lead to disconnection of the clip and/or the spring from the rail.
FIG. 4 of this Mandusky et al. patent shows a symmetric rail with opposing upper side edges, but the retention clip again only has one end secured to one upper side edge of the rail. The other side edge of the rail includes indentations for receiving projections formed on the other end of the retention clip. This construction of the rail appears more secure because both ends of the clip are held. However, the formation of these indentations in the rails requires an extra manufacturing step, as does the formation of the projections in the retention clips. These additional manufacturing steps add additional costs to the box spring.
Also, forming the indentations along the entire length of the rail is relatively costly when considering that only a small number of the indentations are actually used to hold retention clips.
Finally, with the projections fit into the indentations, the clips are no longer slidable along the frame rail after final connection.